linux-kernel - [PATCH 0/2] KVM: X86: Don't reset mmu context when changing PGE or PCID

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Message-Id: <20210919024246.89230-1-jiangshanlai@gmail.com>
Date:   Sun, 19 Sep 2021 10:42:44 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org,
        Lai Jiangshan <laijs@...ux.alibaba.com>
Subject: [PATCH 0/2] KVM: X86: Don't reset mmu context when changing PGE or PCID

From: Lai Jiangshan <laijs@...ux.alibaba.com>

This patchset uses kvm_vcpu_flush_tlb_guest() instead of kvm_mmu_reset_context()
when X86_CR4_PGE is changed or X86_CR4_PCIDE is changed 1->0.

Neither X86_CR4_PGE nor X86_CR4_PCIDE participates in kvm_mmu_role, so
kvm_mmu_reset_context() is not required to be invoked.  Only flushing tlb
is required as SDM says.

The patchset has nothing to do with performance, because the overheads of
kvm_mmu_reset_context() and kvm_vcpu_flush_tlb_guest() are the same.  And
even in the [near] future, kvm_vcpu_flush_tlb_guest() will be optimized,
the code is not in the hot path.

This patchset makes the code more clear when to reset the mmu context.
And it makes KVM_MMU_CR4_ROLE_BITS consistent with kvm_mmu_role.

Lai Jiangshan (2):
  KVM: X86: Don't reset mmu context when X86_CR4_PCIDE 1->0
  KVM: X86: Don't reset mmu context when toggling X86_CR4_PGE

 arch/x86/kvm/mmu.h | 5 ++---
 arch/x86/kvm/x86.c | 7 +++++--
 2 files changed, 7 insertions(+), 5 deletions(-)

-- 
2.19.1.6.gb485710b